The aim of the present study was to evaluate the presence and potential toxic effects of plastic fragments(< 400μm) of polyethylene and polypropylene on the Pacific oysterCrassostrea gigas.Oysters were exposed toenvironmentally relevant concentrations (0, 0.008, 10, 100μg of particles/L) during 10 days, followed by adepuration period of 10 days in clean seawater. Effects of microplastics were evaluated on the clearance rate oforganisms, tissue alteration, antioxidant defense, immune alteration and DNA damage. Detection and quanti-fication of microplastics in oyster's tissues (digestive gland, gills and other tissues) and biodeposits using infraredmicroscopy were also conducted. Microplastics were detected in oyster's biodeposits following exposure to alltested concentrations: 0.003, 0.006 and 0.05 particles/mg of biodeposits in oysters exposed to 0.008, 10 and100μg of particles/L, respectively. No significant modulation of biological markers was measured in organismsexposed to microplastics in environmentally relevant conditions.